Brachiopods

Brachiopods have a very long history of life on Earth (at least
550 million years). They first appear as fossils in rocks of
earliest Cambrian age, and their descendants survive, albeit
relatively rarely, in today's oceans and seas. They were particularly
abundant during the Palaeozoic Era (248 to 545 million years
ago), and are often the most common fossils in rock of that age.

The brachipod Goniorhynchia boueti.

Brachiopods are marine animals belonging to their
own phylum, Brachiopoda, of the animal kingdom. Modern
brachiopods occupy a variety of sea-bed habitats ranging from
the Tropics to the cold waters of the Arctic and, especially,
Antarctic.

Brachiopods are virtually defenceless and their shell, enclosing
the animal's organs, is their only protection. Most are permanently
attached by a fleshy stalk (the pedicle) to a hard, sea-floor
surface, such as a rock outcrop, boulder or some other shell,
and are incapable of actively pursuing food.

The main features of a brachiopod shell

The main features of a brachiopod hinge

A few species can attach themselves directly to soft sediment
and others remain unattached. The pedicle is the only soft tissue
that protrudes outside the shell which opens and closes to allow
food-bearing currents of water to pass through it.

Wide-hinged spiriferid brachiopods (below left) have been
likened to birds. For example, in China, the common name of such
forms translates as 'stone swallows'. There they are boiled
in water with various herbs to produce medicinal potions and
powders.

Spirifer (Carboniferous).

Pentamerus oblongus (Silurian).

Unusually preserved Pentamerus oblongus have led to
the rock in which they occur being called 'Government Rock' (above right).
The original shell material of the brachiopods has dissolved
away leaving arrow-like slits like the symbol used for Government
bench-marks and on prison uniforms.